Non-Electro-Optic Phase Holograms in Lithium Niobate Crystals: Absorption Holograms generated by High-Temperature Recording are linked to Broad-Band Phase Holograms through the Kramers-Kronig Relations

摘要

Permanent reversible diffraction gratings with refractive-index modulations of up to 10~(-4) and with a grating vector perpendicular to the polar axis are realized in doped LiNbO_3 crystals by making use of high-temperature recording and charge compensation. The index changes do not result from light-induced space-charge fields and the linear electro-optic effect. They are linked to fixed high-contrast absorption gratings of filled and empty electron traps, e.g. Cu~+ and Cu~(2+) ions, via the Kramers-Kronig relations.